/*
 * Copyright 2017 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */
package io.netty.util.internal;

import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.NoSuchElementException;

public final class EmptyPriorityQueue<T> implements PriorityQueue<T> {

  private static final PriorityQueue<Object> INSTANCE = new EmptyPriorityQueue<Object>();

  private EmptyPriorityQueue() {
  }

  /**
   * Returns an unmodifiable empty {@link PriorityQueue}.
   */
  @SuppressWarnings("unchecked")
  public static <V> EmptyPriorityQueue<V> instance() {
    return (EmptyPriorityQueue<V>) INSTANCE;
  }

  @Override
  public boolean removeTyped(T node) {
    return false;
  }

  @Override
  public boolean containsTyped(T node) {
    return false;
  }

  @Override
  public void priorityChanged(T node) {
  }

  @Override
  public int size() {
    return 0;
  }

  @Override
  public boolean isEmpty() {
    return true;
  }

  @Override
  public boolean contains(Object o) {
    return false;
  }

  @Override
  public Iterator<T> iterator() {
    return Collections.<T>emptyList().iterator();
  }

  @Override
  public Object[] toArray() {
    return EmptyArrays.EMPTY_OBJECTS;
  }

  @Override
  public <T1> T1[] toArray(T1[] a) {
    if (a.length > 0) {
      a[0] = null;
    }
    return a;
  }

  @Override
  public boolean add(T t) {
    return false;
  }

  @Override
  public boolean remove(Object o) {
    return false;
  }

  @Override
  public boolean containsAll(Collection<?> c) {
    return false;
  }

  @Override
  public boolean addAll(Collection<? extends T> c) {
    return false;
  }

  @Override
  public boolean removeAll(Collection<?> c) {
    return false;
  }

  @Override
  public boolean retainAll(Collection<?> c) {
    return false;
  }

  @Override
  public void clear() {
  }

  @Override
  public void clearIgnoringIndexes() {
  }

  @Override
  public boolean equals(Object o) {
    return o instanceof PriorityQueue && ((PriorityQueue) o).isEmpty();
  }

  @Override
  public int hashCode() {
    return 0;
  }

  @Override
  public boolean offer(T t) {
    return false;
  }

  @Override
  public T remove() {
    throw new NoSuchElementException();
  }

  @Override
  public T poll() {
    return null;
  }

  @Override
  public T element() {
    throw new NoSuchElementException();
  }

  @Override
  public T peek() {
    return null;
  }

  @Override
  public String toString() {
    return EmptyPriorityQueue.class.getSimpleName();
  }
}
